Headspacing adjusting device for firearms



y 4,1953 (3. w. GILLIGAN 2,645,160

HEADSPACING ADJUSTING DEVICE FOR FIREARMS Filed March 10, 1948 Curl VV. Gilli tu-L properly assemble the Patented July 14, 1953 OFFICE HEADSPACING ADJUSTING DEVICE FOR FIREARMS Carl W. Gilligan, East Longmeadow, Mass. Application March 10, 1948, Serial No. 14,139

V Claims.

(Granted under The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to a device whereby the headspace of the bolt of a firearm may be readily adjusted so that such bolt will properly support a cartridge.

maintained, rupture of the cartridge case with consequent damage to the firearm is inevitable.

A common fault of nearly all firearms is the inconvenience in adjusting theheadspace of such firearms. Heretofore substantially all firearms have'been provided with fixed locking lugs and correspondingly fixed locking shoulders so that no adjustment of the headspace of the bolt was possible and accordingly the related components of a firearm had to be manufactured to within exceedingly fine tolerance dimensions in order to breech mechanism so that the correct headspace could be obtained.

Accordingly it is an' obje'ct of this invention to provide adevice whereby the headspace of a firearm can be readily adjusted to obtain the optimum headspace setting without the-necessity of selective assembly and hand fitting of the related breech elements affecting the headspace.

A particular object of this invention is to provide a headspace adjusting device fora firearm such as disclosed in U. S.

Birkigt. v

Another object of this invention is to provide means foradjustably changing the headspace settin of a firearm which is positively locked Patent No. 2,199,872 to whenso set. i

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which-i Fig. 1 ma fragmentary longitudinal sectional view of a firearm embodying this invention showing the locking element'of the firearm in engagement with the'locking shoulder of this. invention.

is an enlarged detail perspective view of Title 35, U. S. Code (1952),

see. 266) the elements of this invention shown in exploded relationship.

Fig. 3 is an enlarged bottom view of the key member embodying this invention showing the manner of securing the elements thereof to the firearm.

This invention to be described in more detail later briefly comprises a key member which is transversely supported in the receiver of a firearm. Such key member has a vertically disposed slot therein one side of which is angularly disposed with respect to the front face of such key member and a plurality of serrations are provided along such side angularly disposed. A look member is insertable in such slot and the lock member is provided with corresponding serrations thereon engageable with the aforementioned serrations. The lock member is likewise provided with a locking surface on the front face thereof which is engageable by the locking element of the firearm. By changing the position of the lock member within the key member; the longitudinal distance from the forward face of such lock member with respect to the locking element may be substantially varied and by this means the headspace of the bolt is correspondingly changed.

A preferred application of this invention is shown in Fig. 1 wherein such device is incorporated in a firearm of the type as disclosed in U. S. Patent No. 2,199,872 to Birkigt. While not limited thereto, the device of this invention is par.- ticularly adapted for use in Such firearm. The firearm shown in such figure comprises a pair of spaced-apart parallel side plates 10 and II which are separated at the rear end by a bufier mechanism housing and by a front spacer (neither of which is shown). Side plates I0 and H and such buiier housing and "front spacer form a receiver M. A bolt Iii is shdably supported within receiver l4 and such bolt is arranged to be unlocked by a gas actuated operating rod (not shown). Bolt I5 essentially comprises a body IS, a pair of parallel slides IT slio'ably mounted on opposite sides of such bolt. Slides ll areconnected at the forward end thereof to boitdfi by a transverse key l8. Bolt 15 is' arranged to be locked toreceiver Hi by a locking'element l9. Such locking element is pivotally mounted on the bottom of bolt l5 as shown in Fig. 1 and is arranged to be raised out of locked relationship with such receiver by parallel slides ll. Lockingelement l9 cooperates with a transverse key member 20 to lock bolt [5 to receiver l4.

Key member 20 is a substantially rectangular member having rounded sides as shown at 2|. Such key member is transversely supported in receiver It by press fitting into suitable openings in side plates Ill and il. Key member 20 is provided with a vertically disposed slot 22 approximately in the center thereof. Such slot,

however, is angularly disposed with. respect to locking element I9 cooperates to lock bolt IE to receiver [4. The rear surface of lock member 26 is provided with the same slope as slot 22 and is likewise provided with a plurality of serrations 23 which correspond to serrations 2d. The length of serrations 28, however, is substantiallysmaller in order to provide adjustment thereof :as will be later described. That portionof lock member 26 being provided with sloped locking surface 2'! is of reduced thickness in order that such portion may fit into the milled portion 25 of key member 20. 7

Lock member 26 is readily assembled to key member 20 by insertion thereof into the slot 22, serrations 28 engaging serrations 24 and the forward portion of lock member 26 engaging the milled section 25 .of key 23 Cooperation of serrations 24 with serrations 28 secures lock member 26 against sideways displacement. A plate 29 of rectangular shape is bolted to the bottom of .each of the members 20 and 26 to hold such members together as shown in Fig. 3. Bolts 36 are utilized for such purpose. Plate 23 is. provided Withe Slot 3! therein which is inclined with respect to the forward edge of such plate to conform to the slope. provided On both slot 22 and 1Qck,. 26.. Inclined slot 3! isnecessary when changing the position, of lock 28. for. adjustment gf the headspace so that the bolts 30 securing lock 25 topllteZS can be traversed along slot 3 1. Inc length of plate 2.9 is adjusted so that it will fit between side plates l0 and H thereby eliminating any possiblesideways movement of transv rse k y memberill...

When key member 20 isassembled to the firearm as shown inl'flig. l, the lockingsurface 2? isdisposed forwardly as shown. Acorrespondins. ckin sur ace 32 i p ov d d n t e end of pivotally mounted locking element l9. and in, the breached pos tion of. he bolt, the locki g sur ac 3 2 c goperates with locking surface 2'1 to secure- 1r l s th qltin such o i on, At sv rsel disposed projection 33 is provided on locking element .Wbi hrmi t w in o a cess 3 i.provided in each of slidesfl'l, The forward edge of projection 33 is sloped as shown inFi'g'. 'l'fwhile a corresponding slopev is provided 'on the forward'edge of recesses 34, such recesses cooperate with projection 33 to raise lockingelemen't] 9 out of engagement'with'transverse key member 28 to unlock bolt ['5 therefrom. Suchis' eflectedby' the rearward 'movement of slides H uponactuation thereof by the gas operating mechanism (not shown).

When bolt I5 is in the breached po's itionpas shown in Fig. 1, with locking element 19 engaginglocking member 26, the forward face of bolt 4 5 shouldproperly support a cartridge 35-contained in the chamber of a barrel 36-which is slidably supported in the forward portion-0f receiver M.

If there is too muchspace between the face of the bolt and the base of the cartridge as may be readily determined by a feeler gage, the position of locking member 26 is moved to correct this deficiency. Locking member 26 is readily disassembled by removal of bolts 30 and such element is then raised to bring serrations '28 out of engagement with serrations 24 whereupon locking member 26 may be moved to a new position and again secured to key member 20 as previously described.

Dueto the wedge construction of locking member26, movement thereof in a transverse direction will accordingly change the longitudinal distance of the'forwardly facing locking surface 27 thereof with respect to a fixed point on the receiver. By proper selection of the number of serrations, the width of such serrations, and knowing the angle of inclination of the slot 22 and locking member 26 with respect to the centerline of the respective members, the amount the front :locking surface'z l moves in a longitudinal direction may be readily determined for each serration. This would of course make it, much simpler for the individual in the field to know exactly how much the locking member is advanced for each serration and knowing the headspace requirements as determined by a feeler gage the proper amount of advancement of surface ZI can bereadily determined. Conversely, if the bolt will not close, that is, if the locking element 19 can not be lowered into engagement with surface 27, the position of locking member 26 may be changed to move such element rearwardly so that locking element 19 can properly engage surface 27. v

It is therefore apparent fromthe foregoing that there is here provided a simple means for accurately adjusting the headspace of a firearm and a means which will remain positively set when once adjusted. Such a device has wide'application in many types of firearms and will eliminate costly fabricating processes due to the fact that ;no longer are various related breech elements required to be made to the exacting dimensions formerly found necessary. I it is, further desired to pointout that when adjustment of the headspace is necessary such adjustment canbe quicklyand readily made without the use of complicated-tools orcostly gages.

Iclaim: U

1. In a firearm of theautomatic type having a receiver, a bolt reciprocable between a locked breeched position and a recoil position within the receiver, a locking element pivotally mounted on the bolt, the improvement comprising a key membermounted in the receiver, and adjustable means in saidkey member adapted to cooperate with the locking element whereby the bolt is positioned for optimumheadspace. p I

2. In a firearm of the automatic type having a receiver, 'a. boltyreciprocable, between a locked breeched. position and a recoil position within the receiver, a locking element pivotally mounted on the bolt, the improvement comprising'a key membermounted in the receiver, .said key memher having aslot therein, a lock member insertable inrsaidrslot, means for adjustably securing said lock memberin said slot, said lock member being constructed and arranged to cooperate with said locking element to longitudinally-position the bolt for headspace adjustment.

3.'In a firearm of 'the automatic type having areceiver, a bolt .reciprocable between alocked breeched position and a recoil position within the receiver, a. locking element pivotally mounted on the bolt, the improvement comprising a key member mounted in the receiver, said key member having a vertical slot therein disposed angularly with respect to the forward face thereof, a lock member adapted to be inserted within said slot, said lock member being narrower than said slot for limited lateral movement therein, and means for securing said lock member within said slot in any one of a plurality of positions, said lock'member cooperating with the locking element to reposition the bolt for headspace adjustment when said lock member is moved laterally.

4. The combination defined in claim 3 wherein said means comprises a plurality of serrations on said lock member engageable with corresponding serrations in said slot.

5. A headspace adjusting device for a firearm of the automatic type having a receiver, a bolt reciproeable between a. locked breech position and a recoilposition within the receiver, and a 20 locking element plvotally mounted on the bolt.

comprising a key member transversely mounted in the receiver, said key member having a slot therein disposed at an acute angle to the forward face thereof, a plurality of serrations on the rear surface of said slot, a lock member insertable in said slot having a lesser width than the length of said slot, said lock member having a plurality of serrations engageable with said first mentioned serrations whereby said lock member may be selectively positioned within said slot, a locking face on said lock member adapted to cooperate with the locking element to lock the bolt to the receiver in the breeched position of the bolt, said angularly disposed slot permitting longitudinal displacement of said locking face of said lock member for headspace adjustment, and means for securing said lock member to said key member.

a a CARL WrGIILIGAN."

No references cited. 

